When a user name is specified, this option indicates that proper authentication has already been done and that no password need be requested. This option may only be used by the super-user or when an already logged in user is logging in as themselves.
Specify the host from which the connection was received. It is used by various daemons such as telnetd(8). This option may only be used by the super-user.
By default, login discards any previous environment. The -p option disables this behavior.
If the file /etc/login.access exists, login checks to see if the user and host pair are specifically allowed or denied access. Login access may also be controlled via the login class, which provides allow and deny records based on time, tty and remote host name.
If the file /etc/fbtab exists, login changes the protection and ownership of certain devices specified in this file.
Immediately after logging a user in, login displays the system copyright notice, the date and time the user last logged in, the message of the day as well as other information. If the file .hushlogin exists in the users home directory, all of these messages are suppressed. This is to simplify logins for non-human users, such as uucp(1).
The login utility enters information into the environment (see environ(7)) specifying the users home directory (HOME), command interpreter (SHELL), search path (PATH), terminal type (TERM) and user name (both LOGNAME and USER). Other environment variables may be set due to entries in the login class capabilities database, for the login class assigned in the users system passwd record. The login class also controls the maximum and current process resource limits granted to a login, process priorities and many other aspects of a users login environment.
Some shells may provide a builtin login command which is similar or identical to this utility. Consult the builtin(1) manual page.